FIG. 1 illustrates a typical structure of a prior-art cylinder type screen printing machine. A number of printing paper sheets 101 are stacked in an automatic paper feeder 1 and are fed by a feed tape 2 one by one towards a cylinder 3. The paper sheets thus fed are positioned ahead of the cylinder 3 as illustrated in FIG. 2 (Paper sheet feed means and positioning means are not shown in the drawing for simplicity.)
With rotation of a crank arm 5, a sector gear 7, connected to the crank arm 5 by a connecting rod 6, is moved to and fro as indicated by double arrow marks in FIG. 1. The sector gear 7 meshes with a gear 8 secured to one end face of the cylinder 3 so that the cylinder 3 may be turned reciprocally in the direction of the arrow mark 102 and in the opposite direction. A screen 9 is mounted on top of the cylinder 3 and is moved in the fore and aft directions (in the directions shown by the arrow marks 103, 104) in timing with the revolution of the cylinder 3 in the forward and reverse directions. Means for reciprocating the screen 9 is known per se and therefore is not illustrated in the drawing for simplicity.
In the synchronized reciprocating movements of the cylinder 3 and the screen 9, the cylinder 3 is turned in a direction opposite to the direction indicated by the arrow mark 102 in FIG. 2 to a position such that a pair of paper gripping claws 4 provided to the cylinder 3 can grip the paper sheet 101 in a well-known manner. With the paper sheet thus gripped by the claws 4, the cylinder 3 is turned in the direction shown by the arrow mark 102. Just when the claws 4 pass through a zone below a squeezee 10 which is mounted vertically movably to a printing machine frame, not shown, the squeezee 10 is lowered to press the screen 9 so that the ink placed on the screen 9 is pressed out for printing a design on the surface of the printing paper 101 being delivered on the underside of the screen 9.
When the cylinder 3 is turned in the direction shown by the arrow mark 102, and the claws 4 are opened ahead of a paper guide 11, as indicated by the double-dotted chain line in FIG. 2, the printed paper sheet 101 is fed over the guide 11 onto a paper sheet discharge table 12 mounted on the discharge side of the cylinder. After the cylinder 3 has been turned a predetermined angle in the direction shown by the arrow mark 102 in FIG. 3, it is turned in the direction opposite to the direction shown by the arrow mark 102. In the similar manner, the screen 9 is moved in the forward direction a predetermined distance in the direction shown by the arrow mark 104 and then moved back in the direction shown by the arrow mark 103. As the screen 9 is moved in the direction of the arrow mark 103, the squeezee 10 is raised away from the screen, at the same time that a doctor 13 mounted vertically movably to the printing machine frame is lowered to scrape the ink on the screen 9 by an interlock device which is also known per se and therefore not shown in the drawing for simplicity.
The cylinder 3 then is rotated again in the direction opposite to the arrow mark direction to start the next printing cycle.
In the prior-art device, mentioned above, the operation of cleaning the side of the screen 9 and removing smudges from the surface of the cylinder 3 has been made by having manual access to the underside of the screen 9 from the back side or by insertion of a special tool. However, when the screen 9 is in the position shown in FIGS. 2 or 3, the space 105 between the screen and the paper feed tape 2 and the space 106 between the screen and the discharge table 12 are rather narrow and tend to obstruct the cleaning operation. Hence, the screen 9 must be removed ultimately to effect such cleaning operation.
Hence, when mounted again in the machine after such cleaning operation, the screen 9 has to be positioned accurately with respect to other component parts, while test printing has also to be performed for color matching or reproduction, with resultingly lowered operational efficiency.
Such cleaning operation may be facilitated if the spaces 105, 106 are broader and, to this effect, the paper feed tape 2 or the discharge table 12 are retreated away from the underside of the screen plate 9. However, the paper feed tape 2 can be retreated only with considerable difficulties because of possible collision with other machine components. Hence, it is desired that the discharge table 12 be retreated to facilitate the cleaning of the screen.